In the brain, transient and lasting changes in the efficacy of synaptic transmission continually shape neuronal circuits to process information. These changes, at least in part, are caused by endocannabinoid (EC) signaling, which has been broadly recognized to control neurotransmitter release at transient (high-intensity phasic) and lasting (low-intensity tonic) time scales, and to additionally mediate long-term synaptic plasticit in multiple brain regions. Although the clinical targeting of the cannabinoid type-1 receptors carries significant therapeutic potential, the neurobiological consequences of EC signaling at distinct timescales are not understood. A major reason for this gap in our knowledge is that at present, no manipulation is available which selectively interferes with phasic or tonic EC signaling. This study aims to fill this gap by following up on our preliminary findings that sugges an unexpected role for neuroligins in EC signaling. Specifically, we have found that neuroligin-3 is essential for tonic but not phasic EC signaling. Neuroligins are postsynaptic cell-adhesion molecules that control diverse, yet synapse-specific, features in central synapses. To examine how the loss of neuroligins affect EC signaling, we will first focus on well-characterized EC-sensitive hippocampal synapses, and second, extend these studies to the circuitry of the ventral tegmental area (VTA), which is known to relay multiple EC-sensitive inputs to shape diverse motivation- and addiction-related behaviors. A better understanding of the molecular specificity underlying EC signaling in distinct timescales and brain regions will enable us to examine their mechanisms and biological significance. Furthermore, by employing a combination of paired-recording electrophysiology and molecular biology, this study will offer novel insights to the loca circuitry of the VTA, which may help to establish a causal relationship between the structure of VTA and the ability of drugs of abuse to elicit prolonged or even irreversible changes within it. PUBLIC HEALTH RELEVANCE: Endocannabinoids (EC) are key regulators of brain function that modulate synaptic transmission in phasic (high-intensity, acute) and tonic (low-intensity, chronic) modes by activating the same receptors; however, the mechanisms and biological significance of the two modes of EC signaling are not understood, and current treatments indiscriminately target both modes. Based on our recent discovery of a selective role for neuroligin-3 in controlling tonic EC signaling, we here propose experiments that will clarify the nature of the two EC signaling modes and facilitate better targeting of these modes in neuropsychiatric diseases.